The highly unsafe primitive unsafeCoerce converts a value from any
type to any other type. Needless to say, if you use this function,
it is your responsibility to ensure that the old and new types have
identical internal representations, in order to prevent runtime corruption.

The types for which unsafeCoerce is representation-safe may differ
from compiler to compiler (and version to version).

Documentation for correct usage in GHC will be found under
unsafeCoerce# in GHC.Base (around which unsafeCoerce is just a
trivial wrapper).

In nhc98, the only representation-safe coercions are between Enum
types with the same range (e.g. Int, Int32, Char, Word32),
or between a newtype and the type that it wraps.